The production of high pressure laminates is well known, having been carried out for many years. Generally, the procedures for forming such laminates involve providing phenolic (i.e., phenol-formaldehyde) resin impregnated paper core sheets and melamine (i.e. melamine-formaldehyde) resin decorative and overlay sheets, and pressing the stacked resin impregnated sheets under heat on the order of 230.degree.-310.degree. F. and under pressure of approximately 800-1600 psi until the resins have become thermoset, thereby providing an extremely hard, attractive and permanent surfacing material known as a "high pressure laminate" meeting NEMA Standards. These high pressure laminates have, for many years, found use as counter and table tops, bathroom and kitchen work surfaces, furniture and cabinet surfacing, wall paneling and partitionings, doors, etc.
Most general purpose decorative high pressure laminates, of about 1/16 inch thickness, are formed of an assembly comprising a top ply of .alpha.-cellulose paper, about 20 lbs. ream weight, impregnated with a partially cured water solution of melamine-formaldehyde condensate; a print ply therebeneath, normally also an .alpha.-cellulose paper, pigment filled, with or without decorative printing on the surface thereof, ranging in weight from 50 to 125 lbs. ream weight and also impregnated with a partially cured amino resin condensate, usually the same melamine resin as used in the overlay ply; and therebeneath a plurality (e.g. six) core plys which are normally 100-130 lb. ream weight kraft paper, impregnated with a water or alcohol soluble partially cured phenolic resin condensate. All of such partially cured resin condensates are referred to as being in the "B-stage", in this stage they are thermoplastic and will flow under heat and pressure during the high heat, high pressure laminating procedure.
The above described assembly is repeated, back-to-back with a separator, each two laminates being separated by a pressing plate die, until a "book" containing, typically, 10 assemblies is obtained. The book is inserted in a high pressure press, and the laminates are cured under the conditions of heat and pressure indicated above. During the pressing cycle, the resins flow and cure, consolidating the individual plys and forming a comprehensive and infusible cross-linked product. After cure, the book is removed from the press and the laminates are separated, trimmed, and their backs or bottom surfaces sanded to improve adhesion for subsequently gluing to various substrates.
In the early years, generally only glossy surface laminates were produced (i.e. using polished molding surfaces), though some attempts were made to provide laminates with some slight surface irregularities to give satin or "textured" finishes. In more recent years it has become increasingly desirable to provide various types of irregular surfaces, ranging from relatively shallow depressions such as textured (e.g., satin, matte or semigloss) surfaces, to relatively deeply "sculptured" or embossed surfaces which have a noticeable three-dimensional effect, such as wood grain, leather, slate, abstract patterns, creative designs, etc. Particularly with the rising costs of natural products, it has become more desirable to provide deeply sculptured high pressure laminates which simulate natural materials such as wood, leather and slate.
Today, high pressure decorative laminates meeting NEMA Standards are manufactured with smooth glossy surfaces, with textured surfaces, or with deeply sculptured or embossed surfaces. In the latter case, a textured surface is usually superimposed on the embossed surface, and these textured surfaces are normally obtained by utilization of a release, parting or separating membrane or sheet of known type which is located, during the laminating operation, between the upper surface of the uppermost laminae and the molding plate die. In the production of deeply sculptured surfaces which simulate natural products such as slate, leather and wood, it is particularly desirable that the textured surfaces be superimposed over the face of the simulated product, since this provides a softer and more naturally appearing product.
In the manufacture of deeply embossed or sculptured surfaces having surface depth variations as great as 7 mils which duplicate natural products such as slate, leather, wood and the like, it has in the past generally been necessary to use either extremely expensive etched steel or stainless laminating die plates or, alternatively, thermoset pressing plate dies such as described in the Michaelson et al U.S. Pat. Nos. 3,303,081 and 3,311,520. While the use of such dies provides the necessary embossing, many simulated natural products, such as wood grain, must have appropriate color in registry with the surface embossing or debossing. Unfortunately, the problem of registration of color and embossing has proven very difficult, conventional registry techniques such as used in the printing industry being unreliable on a consistent basis in the manufacture of high pressure laminates, and also being extremely expensive, often involving complex electronic sensing equipment.
Other methods of providing laminates having registered color and texture having utilized valley printing, namely the inking of high portions of an engraved plate and pressing into the resin while curing. This operation, as well as the mechanical registration of an embossing roll or plate with a print, is difficult to carry into production and/or does not always give a uniform product. In addition, inks may not be compatible with or as durable as the base resin in which case the product will not meet NEMA Standards.
In more recent years, a number of other techniques have been developed in an attempt to solve the problems of registration of color and embossing in the manufacture of deeply sculptured high pressure laminates. Certain of these techniques have been found to be highly useful in the preparation of certain specific types of configuration, e.g. see U.S. Pat. Nos. 3,700,537 and 3,698,978. Other recent techniques have been more versitile from the viewpoint of the design of the product (note, e.g., U.S. Pat. Nos. 3,814,647; 3,732,137; 3,802,947 and 3,661,672), but some of these recent techniques have been less than fully desirable because they require special materials and/or are difficult to carry out successfully with the result that the products are depressions such as textured (e.g., satin, matte or semigloss) surfaces, to relatively deeply "sculptured" or embossed surfaces which have a noticeable three-dimensional effect, such as wood grain, leather, slate, abstract patterns, creative designs, etc. Particularly with the rising costs of natural products, it has become more desirable to provide deeply sculptured high pressure laminates which simulate natural materials such as wood, leather and slate.
Today, high pressure decorative laminates meeting NEMA Standards are manufactured with smooth glossy surfaces, with textured surfaces, or with deeply sculptured or embossed surfaces. In the latter case, a textured surface is usually superimposed on the embossed surface, and these textured surfaces are normally obtained by utilization of a release, parting or separating membrane or sheet of known type which is located, during the laminating operation, between the upper surface of the uppermost laminae and the molding plate die. In the production of deeply sculptured surfaces which simulate natural products such as slate, leather and wood, it is particularly desirable that the textured surfaces be superimposed over the face of the simulated product, since this provides a softer and more naturally appearing product.
In the manufacture of deeply embossed or sculptured surfaces having surface depth variations as great as 7 mils which duplicate natural products such as slate, leather, wood and the like, it has in the past generally been necessary to use either extremely expensive etched steel or stainless laminating die plates or, alternatively, thermoset pressing plate dies such as described in the Michaelson et al U.S. Pat. Nos. 3,303,081 and 3,311,520. While the use of such dies provides the necessary embossing, many simulated natural products, such as wood grain, must have appropriate color in registry with the surface embossing or debossing. Unfortunately, the problem of registration of color and embossing has proven very difficult, conventional registry techniques such as used in the printing industry being unreliable on a consistent basis in the manufacture of high pressure laminates, and also being extremely expensive, often involving complex electronic sensing equipment.
Other methods of providing laminates having registered color and texture having utilized valley printing, namely the inking of high portions of an engraved plate and pressing into the resin while curing. This operation, as well as the mechanical registration of an embossing roll or plate with a print, is difficult to carry into production and/or does not always give a uniform product. In addition, inks may not be compatible with or as durable as the base resin in which case the product will not meet NEMA Standards.
In more recent years, a number of other techniques have been developed in an attempt to solve the problems of registration of color and embossing in the manufacture of deeply sculptured high pressure laminates. Certain of these techniques have been found to be highly useful in the preparation of certain specific types of configuration, e.g. see U.S. Pat. Nos. 3,700,537 and 3,698,978. Other recent techniques have been more versitile from the viewpoint of the design of the product (note, e.g., U.S. Pat. Nos. 3,814,647; 3,732,137; 3,802,947 and 3,661,672), but some of these recent techniques have been less than fully desirable because they require special materials and/or are difficult to carry out successfully with the result that the products are provided the conventional bottom pressing plate 10 having a flat, but unfinished surface; the conventional plurality of phenolic resin impregnated paper core sheets 12, a conventional amino resin impregnated colored print sheet 14, the overlay sheet 16, a conventional parting or release layer 18, and the sculptured or embossed pressing plate die 20.
The overlay sheet 16 differs from the conventional melamine resin impregnated .alpha.-cellulose paper impregnated overlay sheet normally used in a high pressure laminate lay-up or assembly in that it is impregnated with an opacifying pigment contained in a conventional melamine resin. The combination of melamine resin and pigment is such that during the pressing operation most of the resin and the pigment will migrate laterally through the overlay sheet from the high pressure areas to the low pressure areas .Iadd.causing a separation of colors .Iaddend.so that in the final laminate the debossed areas will be relatively free of pigment in the overlay sheet so that the print sheet therebeneath will be visible, while in the embossed areas the pigment will be relatively concentrated so as to mask the print sheet therebeneath.
The lightweight overlay sheet 16 is prepared in the normal manner except that a finely divided opacifying pigment is utilized with the melamine resin. Thus, the lightweight .alpha.-cellulose paper is impregnated with the melamine resin containing the selected pigment; however, the pigment does not become embedded in the individual cellulose fibers to any significant degree and does not become bound to the cellulose of the paper, but it does lie between the cellulose fibers. The amount of pigment in the melamine resin is a function of the color and hiding power of the pigment selected, although typically they will be used in an amount of 0.5 to 10% by weight of pigment based on the resin impregnating solution.
Preferably the pigments are predispersed in water, since this eliminates milling or grinding in conjunction with the resin, which has a tendency to advance the resin cure in an undesirable manner. After predispersing the pigments in water, the dispersion is mixed with the normal type of melamine resin solution, e.g. a 10-90 mixture of isopropyl alcohol and water to which normal adjuvants are added. The normal impregnating procedures are used by passing the .alpha.-cellulose paper through the resin solution containing the dispersed pigment in order to saturate the paper, and then wiping excess liquid from the surface of the paper, and finally drying in an oven at 250.degree.-350.degree. F.
In order to obtain the objectives of lateral flow of resin and pigment during the pressing operation, it is normally preferred that the resin content in the dried overlay sheet be 65-70%, that the volatile content be 6-10%, and that the flow* be 7-35%. Higher flow results in undesirably greater transparency in the debossed portions of the laminate so that there is undesirably high show-through of the underlying print sheet; if sufficient flow is not provided, results will be undesirable in that sufficient contrast will not be provided. Accordingly, it is preferred that flows of 7-15% be provided, since these produce the most satisfactory results. FNT *flow is measured by weighing 12 impregnated paper disks of 15/8 inches diameter, laminating them at 305.degree. F. and 1000 psi, removing the flash from the circumference, and calculating the weight loss as follows:
FLOW=Weight loss.times.100/Original Weight
It has been determined that the degree of flow is critical, although the degree of flow to obtain success is also dependent on the depth of the debossing elements of the pressing plate die so that with greater depth of the debossing portions of the die, the degree of flow may be less, while with shallower debossing portions of the die, the degree of flow must be greater. If flow is too low, the print sheet color will not show through; if the flow is too high, most of the color flows away and the color becomes diffused.
Increasing the resin and/or volatile content will increase the flow. If the volatile contents are too high causing increased flow, the surface may "milk out" causing too low a resin content in the debossing portions and thereby giving an unsatisfactory product in which the debossed portions are dry and insufficiently hard and resistant. The flow is regulated by a combination of resin content, volatile content and by the temperature at which the paper is dried. Those having normal skill in the art will be able to provide a flow within the range of 7-35% based on current knowledge.
With regard to the nature of the sculptured pressing plate die 20, any such plate may be used. For example, one may use an expensive machined or etched steel or stainless steel plate, or one may use a molding plate of the type described in the Jenkins Pat. No. 2,606,855, or the Michaelson et al U.S. Pat. Nos. 3,303,081 or 3,311,520. Also, one may use a thin, embossed, impregnated separator sheet having a nonstick facing of the type disclosed in the Scher et al U.S. Pat. No. 3,674,619, as the embossing surface, in which case the release layer 18 may be eliminated along with the sculptured printing plate die 20, though a flat pressing plate of the nature of pressing plate die 10 will be used to back up the thin, embossed, impregnated separator sheet. One may also use a texturizing film of the type disclosed in the Ungar et al U.S. Pat. No. 3,761,338.
In those instances where a release or parting layer 18 is used, such layers may be selected from those commercially available. These release layers 18 usually provide the dual function of imparting a textured finish to the laminate and also preventing adhesion of the upper surface of the laminate, i.e., the overlay layer 16, to the sculptured pressing plate die 20. Among the release sheets 18 commercially available may be mentioned aluminum foil, silicone resin or silicone oil treated paper, "Quillon" treated paper, fluorocarbon resin treated paper, sodium alginate treated paper, paper-aluminum foil laminate, parchment or glassine papers, etc. Any of these materials may be used as the release layer 18, so long as the non-adherent surface of the release layer 18 is facing the overlay 16.
The print layer 14 may be of the conventional type, either of one color or a plurality of colors. The color may be applied to the upper surface, or it may be internally applied. As indicated above, the print sheet will normally comprise .alpha.-cellulose paper impregnated with melamine resin and dye or pigment. The color of the print sheet is chosen for its desired contrast to the pigment used on the overlay sheet.
The plurality of core sheets 12 will normally comprise kraft paper impregnated with phenolic resin in accordance with usual practice. The pressing plate die 10, located immediately below the core sheets 12, may comprise a simple metallic plate, such as is conventionally used.
The lay-up or assembly or composite is cured using a normal pressing cycle at 800-1200 psi and 260.degree.-310.degree. F. for 45-90 minutes, the press time given assuming starting with a cold press and ending cold.
During pressing, the melamine resin melts, flows and then cures to a hard, infusible state. When the press is opened a pleasing texture is present with pigment concentrated in the embossed areas and the print sheet showing through at the debossed areas. It is clear that the pigment and most of the resin move laterally from the high pressure areas to the low pressure areas and, in the product, varying amounts of the print sheet color show through, depending on the thickness of the overlay layer, which in turn depends on the varying pressure from point-to-point, which in turns depends on the design in the embossed press plate.
Referring to FIG. 2 there is shown a small portion of a cross-section of a laminate produced in accordance with the present invention. Simulated natural products, such as leather and wood, having mottled irregular type patterns, are particularly suited to be formed by the present technique. From FIG. 2 it is seen that in the debossed portion the overlay 16 is relatively thin at 164 and the print layer 14 can be seen at portion 144 through the relatively transparent portion 164 of the overlay sheet 16. To the contrary, at the embossed portions the overlay sheet 16 is relatively thick at portions 162 and the pigment, having migrated from portion 164, is relatively dense and so the print layer 14 at portion 142 is not visible through opaque portion 162 of the overlay sheet 16. Between the two extremes there is a gradual transition.
The product is provided with embossed areas and debossed areas by pressing against the sculptured pressing plate die 20. The resulting laminate has the color of the pigment in the overlay sheet 16 at the embossed portions 162, and at the debossed portions has the color of the print sheet 14 as seen through the transparent portion 164 of the overlay sheet 16. In general, it will be understood that any combinations of print paper color and pigment color in the overlay 16 are possible with the result being a high pressure laminate having areas with contrasting color and surface configuration in exact registration.
The above process is not limited to high pressure laminates, but is equally applicable to the so-called low pressure board where surface sheets are applied directly to particle board.